Since the conventional liquid crystal display devices are thin and consume a low amount of power, they find wide application in a variety of field including portable electronic information apparatuses such as cellular phones, and help spawn new markets.
However, market requirements are accordingly increasingly demanding year after year, and, with the advent of contending technologies such as electroluminescence (EL) or electronic paper, liquid crystal display devices are required to offer an advantage of their own and high display quality. It is under this background that semi-transmissive liquid crystal display devices, in particular, have been keenly sought after, because they have good visibility even in strong outside light or in a dark place, which cannot be provided by the electroluminescence (EL) or electronic paper.
Some semi-transmissive liquid crystal display device are structured as follows. A reflective display electrode (a reflective electrode) is formed in part on a transparent display electrode (a transparent electrode) of a transmissive liquid crystal display device. In this case, however, since the reflective optical path length is twice the transmissive optical path length, it is impossible to offer high display quality in both transmissive and reflective portions. To address this problem, Patent Publication 1 discloses a technique of improving display quality in both transmissive and reflective portions by optimizing the transmissive optical path length and the reflective optical path length by forming a depressed area at the center of a pixel region on an electrode substrate so as to form a transmissive portion and providing a reflective electrode around the transmissive portion. Hereinafter, such a structure is referred to as a TFT multi-gap structure.
FIG. 5 is a plan view schematically showing a pixel portion in a conventional TFT multi-gap structure, and FIG. 6 is a sectional view of FIG. 5, taken along line C-C.
As shown in FIG. 5, in a liquid crystal display element 100 having the TFT multi-gap structure, pixel portions are provided one for each region surrounded by adjacent gate conductors 101 and adjacent source conductors 102, so that a plurality of pixel portions are arranged in a matrix. Each pixel portion has a transmissive region 103 at the center thereof and a reflective region 104 around the transmissive region 103. To form a multi-gap, there is provided a tapered region 105 (shown in FIG. 6) near the boundary between the transmissive region 103 and the reflective region 104, where there is a height difference between resin layers. This tapered region 105 does not contribute to transmission or reflection, and is practically an ineffective display region.
On the other hand, to deal with the above-described problem that the reflective optical path length becomes twice the transmissive optical path length, a technique of forming a cell gap of transmissive/reflective portions on the opposing substrate side has been adopted in recent years. Hereinafter, such a structure is referred to as an opposing layer multi-gap structure.
FIG. 7 is a plan view schematically showing a pixel portion in a conventional opposing layer multi-gap structure, and FIG. 8 is a sectional view of FIG. 7, taken along line D-D.
As shown in FIG. 7, in a liquid crystal display element 200 having the opposing layer multi-gap structure, pixel portions are provided one for each region surrounded by adjacent gate conductors 201 and adjacent source conductors 202, so that a plurality of pixel portions are arranged in a matrix. In each pixel portion, a transmissive region 203 and a reflective region 204 are arranged, as seen in a plan view, one in an upper part and the other in a lower part of the pixel.
With this opposing layer multi-gap structure, there is no need to form a height difference in the part where the transmissive regions 203 of the adjacent pixel portions are adjacent to each other, and there is a need to form a height difference in the part where the transmissive region 203 and the reflective region 204 are adjacent to each other. When such a height difference is formed between the adjacent pixel portions, it is possible to form a tapered region 205 (shown in FIG. 8) producing the height difference over an ineffective display region in a conductor portion lying between the pixel portions on the TFT substrate.
Thus, this opposing layer multi-gap structure makes it possible to extend a usable effective display region near the conductor portion. In addition, only one of the four sides of the transmissive portion, which is rectangular as seen in a plan view, serves as a tapered region (an ineffective display region), where there is a height difference between resin layers. This helps reduce structural waste, and makes it possible to increase the total aperture ratio, that is, the sum of aperture ratios in the transmissive and reflective regions.
Patent Publication 1: JP-A-H11-316382